Traditionally: Red, Yellow, and Blue are the only 3 colours that can not be mixed or created with the combination of other colours. All colours are created from Red, Yellow, and Blue.
Green, Orange, and Violet (Purple) are secondary colours. These colours are formed by mixing 2 of the primary colours.
These are colours such as: Blue-Green, or Yellow-Orange. These colours are made by mixing 1 primary colour and 1 secondary colour together.
Terminology & What Colours Do
Base Colour: Is the dominant, main colour you are attempting to mix.
Tints: A mixture of colour and white, can also increase lightness. Tone: Changing the tone of the base colour is done by using grey.
Red: Lights dark colours.
Blue: Darkens light colours.
Yellow: Lightens dark colours.
Green: Darkens light colours.
Black: Darkens any colour, may also kill brightness.
White: Lightens any colour.